DE102015101817B4 - PIEZOELECTRIC DEVICE, PIEZO ACTUATOR, HARD DRIVE AND INKJET PRINTER - Google Patents

Abstract

Piezoelectric device with a piezo element comprising a piezo layer and electrode layers, between which the piezo layer is arranged, and with a driver circuit that applies an electric driver field with alternating current via the electrode layers to the piezo layer, the polarizability γ of the piezo layer when an electric field is applied up to Saturation polarization is less than 1 × 10-9 (C / (V · m), characterized in that the driver circuit has a means which sets the minimum value of the driving electric field to be greater than the positive electric coercive field of the piezo layer, and a means which sets the Maximum value of the electric driver field to less than (Pm '(maximum value of the polarization) - Pr' (quasi-residual polarization)) / (1 × 10-9), the polarizability y = (Pm (saturation polarization) - Pr (residual polarization )) / Ed (maximum value of the applied electric field).

Description

Field of Invention

The present invention relates to a piezoelectric device comprising a piezo element with a piezo layer and a drive circuit which controls an electric drive field to be applied to the piezo layer, and a piezo actuator using the piezoelectric device, as well as a hard disk drive and an ink jet printer apparatus with the piezo actuator.

State of the art

Recently, the practical application of the piezo element using thin-film piezoelectric materials in place of solid piezoelectric materials is advancing. Examples of this are gyro sensors, pressure sensors, pulse wave sensors, shock sensors or microphones as piezoelectric sensors based on the piezoelectric effect, in which the force acting on the piezo layer is converted into a voltage. There are also hard disk drive head sliders and ink jet printheads as piezo actuators based on the inverse piezoelectric effect, in which the piezo layer is deformed when an electric field is applied to the piezo layer. Loudspeakers, buzzers, resonators, etc. should also be mentioned, which also use the inverse piezoelectric effect.

In addition, reducing the thickness of a piezoelectric material makes it possible to downsize the elements, so that the application range thereof is expanded and productivity is increased, since a large number of the element can be fabricated at one time on one substrate. Also, there are many performance benefits such as increasing sensitivity when it is a sensor.

Prior art document

Patent literature

Patent Literature 1: Japanese Published Unexamined Patent Application No. JP H05-114760 A

Summary of the invention

Task

When an electric field is applied to a piezoelectric body, polarization takes place on the piezoelectric body, so that a hysteresis is observed as the course of a change in the direction of polarization. In the case of the piezoelectric body, in which the change in polarization is small compared to the electric field to be applied and a hysteresis with a large squareness ratio is shown, there is no significant change in the piezoelectric properties despite the change in value of the electric field to be applied. In the case of the piezoelectric body, on the other hand, in which a hysteresis with a low squareness ratio is shown, problems arise that, depending on the conditions of the electric field to be applied, insufficient piezoelectric properties are obtained, or that permanent drive of the piezo element increases the likelihood of polarization deterioration or the reduction in resilience is increased. In general, the squareness ratio of the thinned piezo layer is smaller compared to the piezoelectric body made of a bulk material. This tendency is particularly pronounced with a piezo layer that does not contain lead.

1 shows a PE (polarization - electric field) hysteresis for the case in which an electric field on the piezo layer with a hysteresis with a relatively small squareness ratio is applied to the positive and negative poles up to the saturation polarization. The electric fields in which the polarization is 0 are positive and negative coercive electric fields Ec + and Ec-, respectively.

With regard to the above-mentioned object, the technique described in Patent Literature 1 shows that the decrease in the degree of polarization with a permanent drive of the piezo actuator both at high temperatures and under high pressure can be overcome by the method when driving a piezo actuator to apply an always positive electric field to a piezoelectric body. Because the process requires a solid piezoelectric material as the piezoelectric body, it can be used in the Use of the method for a thin piezo layer can easily lead to the destruction of the membrane, even if the piezo layer is applied an electric field in which no deterioration in polarization occurs. Incidentally, if an electric field smaller than the coercive electric field is applied, it may contribute to the reduction in polarization deterioration, but it may not achieve a sufficient amount of displacement.

The present invention was made in view of the objects of the above-mentioned prior art and its aim is to control the electric drive field to be applied to the piezo layer by the drive circuit of a piezoelectric device and thereby a good performance in due to the dielectric properties of the piezo layer used of the piezoelectric device.

Solution of the task

For the realization of the above-mentioned goal, the piezoelectric device according to the invention is concerned with a piezo element comprising a piezo layer and the electrode layers, between which the piezo layer is arranged, and with a driver circuit that applies an electric driver field with alternating current to the piezo layer via the electrode layers , wherein the polarizability y of the piezo layer when an electric field is applied up to saturation polarization is less than 1 × 10 ^-9 (C / (V m)), and the driver circuit means that the minimum value of the electric driver field is greater than that sets positive electric coercive field of the piezo layer, and a means which sets the maximum value of the electric driving field to less than (Pm '(maximum value of polarization) - Pr' (quasi-residual polarization)) / (1 × 10 ^-9 ). Here polarizability is: y = (Pm (saturation polarization) - Pr (residual polarization)) / Ed (maximum value of the electric field to be applied), where the unit of polarization is (C / m ² ) and the unit of the electric field is (V / m) .

As described above, in a piezoelectric body whose saturation polarizability y is close to 0 and which exhibits a hysteresis with a large squareness ratio, no significant change in the obtained piezoelectric properties occurs despite the change in the value of the electric field to be applied.

In the piezoelectric device, the extent of the displacement of the piezo element is expanded by setting the minimum value of the electrical driver field to be applied to the piezo layer to be greater than the positive electrical coercive field, because the polarization directions of the crystal particles configuring the piezo layer are thereby coordinated with one another. Furthermore, a greater degree of displacement can be achieved by setting the maximum value of the electric driver field to less than (Pm '(maximum value of polarization) - Pr' (quasi-residual polarization)) / (1 × 10 ^-9 ) because a shift is achieved which is due to the rotation of the electrical dipoles in the domain of the crystal particles configuring the piezo layer.

2 shows a PE hysteresis of the piezo layer, in which the hysteresis shows itself with a relatively low squareness ratio, when an electric field is applied, in which the polarization is not brought to saturation. The maximum value of the polarization Pm 'represents the extent of the polarization of the piezo layer when the maximum value Ed of the electric field to be applied is applied in the piezo layer, while the quasi-residual polarization Pr' shows the extent of the polarization, the PE hysteresis when applied up to Maximum value Ed of the electric field to be applied intersects the axis of the electric field to be applied = 0. Furthermore, the maximum value of the electric driver field is set to be smaller than the value at which the electric field to be applied is (Pm '- Pr') / (1 × 10 ^-9 ), because 1 × 10 ^-9 corresponds to the polarizability y of the piezo layer , and the piezo layer can be destroyed by the electrostriction effect if the electric field is applied to a piezo layer whose (Pm '- Pr) / Ed is greater than 1 × 10 ^-9 .

The piezo layer of the piezoelectric device according to the invention has an electric coercive field on the positive and the negative side of the electric field. The drive circuit of the piezoelectric device preferably comprises a means which applies a positive electric field in the direction with a small absolute value of the electric coercive field and a negative electric field in the direction with a large absolute value of the electric coercive field. Because this allows the piezoelectric properties of the piezo layer to be driven in a larger area of the electric field, the extent of the displacement of the piezo layer can be further expanded.

The driver circuit of the piezoelectric device according to the invention preferably comprises a means which sets the minimum value of the electrical driver field to more than five times the positive electrical coercive field of the piezo layer and the maximum value of the electrical driver field to less than fifty times the positive electrical coercive field of the piezo layer. Because this increases the displacement which can be attributed to the rotation of the electrical dipoles in the domain of the crystal particles configuring the piezo layer, the extent of the displacement of the piezo layer can be further expanded.

The piezo layer of the piezoelectric device according to the invention preferably consists of potassium sodium niobate. The effect of the increased amount of displacement by adjusting the driving electric field is clearly evident because the coercive electric field of potassium sodium niobate is smaller than that of other materials and the domain in the crystal particles is small. Potassium sodium niobate can also contain Mn, Li, Ta, Ba, Sr, Zr as additives.

The piezo actuator according to the invention has the piezoelectric device shown in the configuration described above. As a piezo actuator, the head arrangement of a hard disk drive, the piezo actuator for an inkjet print head, etc. should be mentioned in this specific respect.

The hard disk drive and the ink jet printing apparatus of the present invention use the piezo actuator described above.

Effect of the invention

The piezoelectric device of the present invention can achieve an increase in the performance of the piezo actuator, whereby a hard disk drive and an ink jet printer apparatus with high performance can be provided.

Figure list

• [1] eine P-E-Hysterese im Sättigungszustand einer Piezoschicht nach der vorliegenden Ausführungsform,
• [2] eine P-E-Hysterese bei dem Vorsättigungszustand einer Piezoschicht nach der vorliegenden Ausführungsform,
• [3] einen Schaltplan für die Stromleitung einer piezoelektrischen Vorrichtung nach der vorliegenden Ausführungsform,
• [4A] einen Aufbauplan für einen Piezoaktor nach der vorliegenden Ausführungsform,
• [4B] einen Aufbauplan für einen Piezoaktor nach der vorliegenden Ausführungsform,
• [5] einen Aufbauplan für ein Festplattenlaufwerk nach der vorliegenden Ausführungsform und
• [6] einen Aufbauplan für einen Tintenstrahldruckerapparat nach der vorliegenden Ausführungsform.

It shows:

• [ 1 ] a PE hysteresis in the saturation state of a piezo layer according to the present embodiment,
• [ 2 ] a PE hysteresis in the presaturation state of a piezo layer according to the present embodiment,
• [ 3 ] a circuit diagram for the power line of a piezoelectric device according to the present embodiment.
• [ 4A ] a construction plan for a piezo actuator according to the present embodiment,
• [ 4B ] a construction plan for a piezo actuator according to the present embodiment,
• [ 5 ] a construction diagram for a hard disk drive according to the present embodiment and FIG
• [ 6th ] is a configuration diagram for an ink jet printer apparatus according to the present embodiment.

Embodiments of the invention

In the following, a preferred embodiment of the present invention is described in detail with reference to the accompanying drawings. Identical or equivalent elements are provided with the same reference symbols in the drawings. Incidentally, the relationship of the position between left and right and up and down is as shown in the drawings. If an explanation is repeated, it will be abbreviated.

(The piezo element)

3 Figure 13 shows an example of a circuit diagram showing the power line of a piezoelectric device 1 according to the present embodiment. The piezoelectric device 1 has a piezo element 80, a driver circuit 20 which controls the electrical driver field of the piezo element 80, a current monitoring circuit 30 which monitors the current value flowing through the piezo element 80, and a switching means 40. The piezo element 80 has a first electrode layer 81, a piezo layer 82 formed on the first electrode layer 81, and a second electrode layer 83 formed on the piezo layer 82. Incidentally shows 3 the piezo element 80 is turned upside down.

The first electrode layer 81 is made of Pt (platinum), for example. The first electrode layer 81 has a thickness of 0.02 μm to 1.0 μm, for example. By making the first electrode layer 81 made of Pt, the piezo layer 82 can be formed with high aligning ability. Metal materials such as Pd (palladium), Rh (rhodium), Au (gold), Ru (ruthenium), Ir (iridium), Mo (molybdenum), Ti (titanium) and Ta (tantalum) or conductive metal oxides can also be used as the first electrode layer 81 such as SrRuO ₃ , LaNiO ₃ , etc. can be used. The first electrode layer 81 can be formed by sputtering method, vacuum evaporation method, printing method, spin coating method, sol-gel method, and so on.

The perovskite compound represented _{by the general formula ABO 3} can be named as the material for the piezo layer 82. The piezo layer 82 preferably consists primarily of (K, Na) NbO ₃ (potassium sodium niobate). The piezo layer 82 exhibits a hysteresis with a relatively small squareness ratio, although the polarizability y at saturation is less than 1 × 10 ^-9 (C / (V · m)). Here polarizability is: y = a (Pm (saturation polarization) - Pr (residual polarization)) / Ed (maximum value of the applied electric field) (see 1 ).

The piezo layer 82 can be formed by sputtering method, vacuum evaporation method, printing method, spin coating method, sol-gel method, and so on. The thickness should be, for example, approximately from 1 µm to 5 µm.

The second electrode layer 83 is made of Pt, for example. The second electrode layer 83 has a thickness of 0.02 μm to 1.0 μm, for example. The metal materials Pd, Rh, Au, Ru, Ir, Mo, Ti, Ta, etc. or also conductive metal oxides such as SrRuO ₃ , LaNiO ₃ etc. can be used as the second electrode layer 83. The second electrode layer 83 can be formed by sputtering method, vacuum evaporation method, printing method, spin coating method, sol-gel method, and so on.

The piezo element 80 can also be covered with a protective film. This can increase the reliability.

In the case of the piezo element 80, a middle layer can be provided between one of the first electrode layer 81 and the second electrode layer 83 or both and the piezo layer 82.

A conductive oxide is used as this middle layer. Above all, SrRuO ₃ , SrTiO ₃ , LaNiO ₃ , CaRuO ₃ , BaRuO ₃ , (La _x Sr ₁ - _x ) CoO ₃ , YBa ₂ Cu ₃ O ₇ , La ₄ BaCu ₅ O ₁₃ , etc. which have high conductivity are preferred and have heat resistance.

The above-described laminate body with the piezo element 80 is formed on a specific substrate. The piezo element 80 does not necessarily have to have this substrate. After the first electrode layer 81, the piezo layer 82 and the second electrode layer 83 have been laminated on the substrate and after the piezo element 80 has been patterned by photolithography, the substrate can be removed by dry etching or the like. In the case of the piezo element 80 with a substrate, the substrate can be cut off after the patterning.

The size of the piezo element 80 in the direction perpendicular to the lamination direction is not necessarily specified, but can be approximately 1.0 mm × 0.3 mm, for example.

The driver circuit 20 has the function of applying a specific electric field to the piezo element 80. For example, in that the driver circuit 20 comprises a charge pump and as in FIG 3 is connected to an external current source 51, the voltage output by the external current source 51 can be amplified and a specific electrical field can be output to the piezoelectric element 80.

As in 3 the piezoelectric device can be represented 1 In addition to the driver circuit 20, they also have a current monitoring circuit 30. The current monitoring circuit 30 applies the electric field to the piezo element 80 and has the functions of monitoring the polarization P and outputting a specific value of the electric field as a signal to the driver circuit 20.

In the piezoelectric device 1 a switching means 40 can also be provided. The switching means 40 has the function of electrically switching between the connections of the driver circuit 20 and the current monitoring circuit 30. The switching means 40 and thereby also the piezo element 80 are normally switched on when the piezoelectric device is put into operation 1 with a current monitoring circuit 30 connected. After the signals EuI and EuII, which are explained below and obtained from the current monitoring circuit 30, are fed back to the driver circuit 20, an action of switching takes place. However, it is also possible to switch over the switching means 40 after a certain period of time and then to carry out the current monitoring action explained below.

The control of the action of the driver circuit 20, the current monitoring circuit 30 and the switching means 40 can also be carried out together in one integrated circuit. When a plurality of piezoelectric devices are used in a piezoelectric system, the drive circuit 20, the current monitoring circuit 30 and the switching means 40 of the individual piezoelectric devices 1 be combined in an integrated circuit.

(The adjustment procedure of the electric driver field)

The driver circuit 20 of the piezoelectric device according to the invention 1 has the mean that sets the minimum value Emin of the electric drive field to be greater than the positive electric coercive field Ec + of the piezo layer 82, and the mean that sets the maximum value Emax of the electric drive field to be less than (Pm '(maximum value of the polarization) - Pr' ( Quasi-residual polarization)) / 1 × 10 ^-9 (C / (V · m)).

Here, 1 × 10 ^-9 (C / (V · m)) is shown as a numerical value that corresponds to the polarizability y. But this applies to the case in which the unit of polarization (C / m ² ) and the unit of the electric field (V / m) are mentioned. In the following description, however, (µC / cm ² ) are used as the unit of polarization and (kV / mm) as the unit of the electric field, so that the critical value of the polarizability y is 0.1.

First, the current monitoring circuit 30 and the piezo element 80 are connected to one another by the switching means 40 in order to apply the electric field to the piezo element 80 and to measure the degree of polarization. The electric field to be applied is obtained from the external power source 52. The electric field to be applied to the piezo element 80 is from 0 kV / mm to the electric field (maximum value Ed of the applied electric field in 1 ), in which the piezo layer 82 is saturated, is increased. After the value has been brought back to 0 kV / mm, it is applied to -Ed, and then returned to Ed again, so that a pendulum operation takes place here. By this operation, the positive coercive electric field Ec + is obtained, and based on this information, the minimum value EII of the electric field to be applied is evaluated to output the electric field to the drive switch 20.

Next, the above-described oscillation operation is performed by gradually increasing the maximum value Ed of the electric field to be applied from the current monitoring circuit 30 to the piezoelectric element 80 by 0.1 kV / mm, with the polarizability y from Pm '(maximum value the polarization) - Pr '(quasi-residual polarization) and is evaluated from the maximum value Ed of the electric field to be applied (see 2 ). Then the maximum of the electric field to be applied is evaluated at which the polarizability y 0.1 is not exceeded in order to define this as the maximum value EuI and then to output the electric field to the driver switch 20.

Next, the driver switch 20 and the piezo element 80 are connected to one another by switching over the switching means 40 from the current monitoring circuit 30 to the driver switch 20. Within the entered range from EII to EuI and depending on the signals from which the piezoelectric device 1 integrating piezoelectric system or depending on the necessary property of the piezoelectric system and on the basis of the conditions set by the driver switch 20, the driver switch 20 regulates Emin and Emax in order to determine the area of the electrical driver field to the piezoelectric element 80.

The piezo element 80 is then driven using the external current source 51 within the range between Emin and Emax.

Of the positive and negative electric coercive fields Ec + and Ec, the direction of the electric field with a small absolute value is preferably positive, the electric field P = O in the positive direction as Ec + and the electric field P = O in the negative direction as Ec- . To drive the piezoelectric element 80, the positive electrical coercive field Ec + is preferably defined as the lower limit value EII of the electrical driver field and the electrical field at γ = 0.1 as the upper limit value EuI of the electrical driver field. This can cause the displacement of the piezoelectric element 80 of the piezoelectric device 1 still to be expanded.

It is even more preferable, when driving the piezo element 80, to define the minimum value Emin of the electric drive field more than five times the positive electric coercive field Ec + of the piezo layer 82 and the maximum value Emax of the electric drive field less than fifty times the positive electric coercive field Ec + of the piezo layer 82. This can cause the displacement of the piezoelectric element 80 of the piezoelectric device 1 still to be expanded.

(The measurement method of the piezoelectric constant)

The piezoelectric constant of the piezoelectric element 80 that makes up the piezoelectric device 1 configured, is measured by the following procedure.

The electric field set to 1 kHz by the power source 51 was applied to the first electrode layer 81 and the second electrode layer 83. The displacement of the piezo element 80 was measured with the aid of a laser displacement measuring device (manufactured by Ono Sokki). The piezoelectric constant (-d31) was then calculated by the following formula (1): $$d_{31}\cong -\frac{H_s^2}{3{\mathrm{L.}}^2}\frac{s_{11p}}{s_{11s}}\frac{\delta }{V}$$

Here, h _s : thickness of the substrate, S _{11, p} : modulus of elasticity of the piezo layer, S _{11, s} : modulus of elasticity of the substrate, L: length of the drive part of the piezo layer, δ: amount of displacement, V: applied voltage.

(The piezo actuator)

4A Fig. 13 shows a construction diagram for a head assembly mounted in a hard disk drive (hereinafter also referred to as HDD) as an example of a piezo actuator using the piezoelectric device of the present invention. As this figure illustrates, the head assembly includes 200 a base plate 9, a load carrier 11, a bend 17, a piezoelectric device 13 (1) which has the first and second piezo elements 13a (80) as drive elements and an element circuit 13b, and a slide 19 with a head element 19a as the main component.

The element circuit 13b has an integrated circuit which comprises a driver circuit, a current monitoring circuit and a switching means. Furthermore, it is also possible to combine several element circuits for controlling a plurality of piezo elements in a single integrated circuit. The element circuit 13b is arranged on the flexible substrate for wiring 15 which forms part of the bend 17. The function of the integrated circuit can, however, also be added solely to the control device of the voice coil motor on the HDD substrate.

The load carrier 11 comprises a proximal end 11b, which is fastened to the base plate 9, for example by electron beam welding, the first and second leaf spring parts 11c and 11d, which taper from the proximal end 11b, the opening 11e, which is between the first and second leaf spring parts 11c and 11d, and the boom main portion 11f extending continuously linearly and tapered from the first and second leaf spring members 11c and 11d.

The first and second piezoelectric elements 13a are each arranged on the flexible substrate for wiring 15, which forms part of the bend 17, with a predetermined spacing. The slide 19 is attached to the tip of the bend 17 and is set in a rotary motion in accordance with the expansion of the first and second piezo elements 13a.

The first and second piezo elements 13a consist of the first and second electrode layers and of the piezo layer which is arranged between the first and second electrode layers. In the piezo actuator of the present invention, high reliability and a sufficient amount of displacement can be achieved because the electric field to be applied, which can achieve the optimal piezoelectric properties of the individual piezo elements, is checked before the electric drive field is set in the piezoelectric device.

4B Fig. 13 is a configuration diagram for the piezo actuator of an ink jet printer head as an example other than the piezo actuator with the above-described piezoelectric device, and shows an application example of the piezo element 80 in the piezoelectric device 1 .

The piezo actuator 300 is configured by laminating an insulating film 23, a lower electrode layer 24, a piezo layer 25, and an upper electrode layer 26 on a substrate 22.

The piezo layer 25 is not deformed if no predetermined discharge signal is supplied and the electric field between the lower electrode layer 24 and the upper electrode layer 26 is not applied. In the pressure chamber 21 with the piezo element, to which no discharge signal is supplied, there is no change in pressure, so that no ink drop is ejected from its nozzle 27.

The piezo layer 25, on the other hand, is deformed when a predetermined discharge signal is supplied and a specific electric field is applied between the lower electrode layer 24 and the upper electrode layer 26. In the pressure chamber 21 with the piezo element to which a discharge signal is supplied, its insulating film 23 is greatly bent. As a result, the pressure in the pressure chamber 21 rises instantaneously, so that ink droplets are ejected from the nozzle 27.

A piezoelectric device is used here as the piezoelectric device of the piezoelectric actuator according to the invention, which sets and applies the electric field that can achieve the optimal piezoelectric properties of the individual piezoelectric elements in order to achieve high reliability and a sufficient degree of displacement.

(The hard disk drive)

5 Fig. 3 shows a layout of a hard disk drive to be used with the in 4A head assembly shown is equipped.

The hard drive 700 has in the housing 60 a hard disk 61 as a recording medium and a head stacker 62 which stores and reproduces magnetic information therein. The hard disk 61 is rotated by an unillustrated motor.

The head stack assembly 62 is composed of a plurality of assemblies laminated in the depth direction of the figure configured by an actuator arm 64 rotatably supported about a shaft by a voice coil motor 63 and a head assembly 65 connected to the actuator arm 64 . At the top of the head assembly 65, the head sliding part 19 is mounted facing the hard disk 61 (see FIG 4A) .

The head assembly 65 ( 200 ) is shaped so that the head element 19a (see 4A) is moved in two stages. A relatively large movement of the head element 19a is controlled by the overall drive of the head assembly 65 and the actuator arm 64 by means of the voice coil motor 63, while a relatively small movement is controlled by the drive of the head slide 19 at the tip of the head assembly 65.

Because the piezoelectric device used for the head arrangement 65 uses the piezoelectric device that sets and applies the electric field that can achieve the optimal piezoelectric properties of the individual piezo elements, high reliability and sufficient accessibility can be achieved.

(The inkjet printer apparatus)

6th shows a construction plan of an in 4B illustrated ink jet printer apparatus equipped with an ink jet print head.

The inkjet printer apparatus 800 is mainly configured with an ink jet print head 70, a body 71, a tablet 72, and a head drive mechanism 73. The piezo actuator 300 is provided on the ink jet print head 70.

The inkjet printer apparatus 800 contains an ink cartridge with the four colors yellow, magenta, cyan and black and is thus configured to allow full color printing. The inkjet printer apparatus 800 Incidentally, it has its own controller plate or the like inside to control the timing control of the ejection of ink at the inkjet printhead 70 and the scanning of the head drive mechanism 73. Further, the body 71 has the tray 72 on the rear side, inside of which there is an automatic sheet feeder (automatic continuous paper feed mechanism) 76 for automatically feeding the recording paper 75 and discharging the recording paper 75 from the front discharge port 74.

By setting and applying the electric field which can achieve the optimum piezoelectric properties of the individual piezo elements in the piezoelectric device used for the piezo actuator of the ink jet print head 70, an ink jet printer apparatus with high reliability and safety can be provided.

Embodiments

In the following, the present invention is explained more concretely on the basis of working examples and comparative examples, although the present invention is not intended to be restricted to the following examples.

(Embodiment 1)

First, the first electrode layer 81, which served as the base film of the piezo layer 82, was formed on a 3-inch substrate made of single crystal Si by a process of crystal growth. This first electrode layer 81 was a Pt film, the film thickness of which was 0.2 µm. The production method in question was the sputtering method, in which the deposition was carried out while heating the substrate to 500 ° C.

A piezo layer 82 was then deposited on the first electrode layer 81 using the sputter target made of the composition of (K _0.5 Na _0.5 ) NbO _{3 (potassium sodium niobate).} The forming method was the sputtering method in which deposition was carried out under the condition of heating the substrate to 750 ° C. as in the first electrode layer 81. The film thickness was 2.0 µm (KNN1).

Subsequently, Pt was deposited as a second electrode layer 83 on the piezo layer 82. As with the first electrode layer 81, the forming process was the sputtering process, but the temperature of the substrate was set to 200 ° C. The film thickness was 0.2 µm.

Then, the lamination structure on the substrate was patterned by the photolithography. The substrate was then removed by the RIE dry etching, thereby fabricating a piezo element 80 having a 0.3 mm × 1.0 mm mobile part.

Next up was a piezoelectric device 1 with a piezo element 80 and with the circuit structure as in 3 configured. As an IC comprising a driver circuit 20, a current monitoring circuit 30 and a switching means 40, an ASIC (application-specific integrated circuit) was used for miniaturization and energy saving.

First, an electric field was applied to the piezo element 80, at which the piezo layer 82 was saturated, whereby 0.44 and 1.02 kV / mm were obtained as positive and negative electric coercive fields Ec- and Ec +, respectively. Consequently, the lower limit EII of the electric field to be applied in this state was about 1 kV / mm. In this case, the polarizability was y = 0.086.

Next, the maximum value Ed of the electric field to be applied was increased gradually by 0.1 kV / mm from the current monitoring circuit 30 to the piezo element 80, with the polarizability y from Pm '(maximum value of the polarization) - Pr' (quasi-residual polarization ) and was evaluated from the maximum value Ed of the electric field to be applied (see 2 ). Namely, as the maximum value Ed of the maximum electric field to be applied at which the polarizability y is not less than 0.1, 64 kV / mm was obtained as the upper limit value EuI of the electric field to be applied.

The lower limit value EII obtained thereby and the upper limit value EuI of the electric field to be applied were inputted as signals from the current monitoring circuit 30 to the driver circuit 20. The switching means 40 was then switched over from the current monitoring circuit 30 to the driver circuit 20. After then assuming the limitations of the piezoelectric system etc. Emin were set to 5 kV / mm and Emax to 52 kV / mm, the piezo element 80 was driven by a sine wave in the range between Emin and Emax.

Incidentally, the piezoelectric properties of the piezoelectric element 80 were evaluated as described above by means of a laser displacement meter (manufactured by Ono Sokki). A sine wave of 1 kHz frequency was applied by Emin and Emax of the above conditions. When measuring the displacement, the piezoelectric constant -d31 was evaluated. The piezoelectric constant -d31 of the piezo element 80 according to embodiment 1 was 37 pm / V.

(Comparative examples 1-1, 1-2 and 1-3)

The configuration and manufacturing process of the piezo element of the piezoelectric device in Comparative Examples 1-1, 1-2, and 1-3 were performed in the same way as in Embodiment 1. The difference, however, was in the setting in the driver circuit in which EII and EuI obtained from the current monitoring circuit define Emin and Emax.

As far as the respective driving electric field was concerned, the condition in Comparative Example 1-1 was that the minimum value Emin of the driving electric field was less than 0 kV / mm (and of course also less than the coercive electric field of the piezoelectric body Ec +). In Comparative Example 1-2, the condition was that the minimum value Emin of the driving electric field was greater than 0 kV / mm and less than the coercive electric field of the piezoelectric body Ec +. In Comparative Example 1-3, the condition was that the maximum value Emax of the electric driver field was greater than the upper limit value EuI, at which the polarizability was y = 0.1. The piezoelectric constant was evaluated in the same manner as in Embodiment 1.

(Embodiment 2)

Using the piezoelectric element 80 having the same property as Embodiment 1, the piezoelectric device was made 1 of the embodiment 2 configured. The size of the two electrical coercive fields that were generated when the PE hysteresis was measured by the current monitoring circuit 30 in the piezoelectric device was checked 1 were obtained. In contrast to the exemplary embodiment 1 one of the two coercive electric fields was defined as Ec + with a small absolute value, the application direction of Ec + being set as the positive direction of the electric field. The piezoelectric constant was determined in the same manner as in the embodiment 1 calculated.

(Embodiment 3)

In the same piezoelectric device 1 As in Embodiment 2, Emin and Emax were set to be greater than five times Ec + and less than fifty times Ec +, respectively, based on the upper and lower limit values EII and EuI obtained from the current monitoring circuit 30. The piezoelectric constant was determined in the same manner as in the embodiment 1 calculated.

(Embodiment 4)

Except that the deposition temperature of the piezo layer 82 was set to 800 ° C, the piezoelectric device became 1 of the embodiment 4 as that of the embodiment 1 configured. The piezoelectric constant was calculated in the same manner as in Embodiment 1. Ec-, Ec +, γ and EuI of the piezo layer 82 (KNN2) were 0.67 kV / mm, 1.26 kV / mm, 0.085 and 65 kV / mm, respectively.

(Embodiment 5)

Using the same piezoelectric element 80 as in Embodiment 4, the piezoelectric device was constructed 1 of the embodiment 5 configured. The current monitoring circuit 30 in the piezoelectric contraption 1 was set in the same manner as in Embodiment 2 in this case. The piezoelectric constant was evaluated in the same manner as in Embodiment 1.

(Embodiment 6)

Using the same piezoelectric element 80 as in Embodiment 4, the piezoelectric device was constructed 1 of the embodiment 6 configured. The driving circuit 20 in the piezoelectric device 1 was set in the same manner as in Embodiment 3 in this case. The piezoelectric constant was evaluated in the same manner as in Embodiment 1.

(Comparative example 2)

Using the same piezoelectric element 80 from Embodiment 4, the piezoelectric device was constructed 1 of Comparative Example 2 configured. The current monitoring circuit 30 in the piezoelectric device 1 was in this case in the same manner as in Comparative Example 1-3 set. The piezoelectric constant was calculated in the same manner as in Embodiment 1.

(Embodiment 7)

Except that the material of the piezo layer 82 was (Bi _0.5 Na _0.5 ) TiO ₃ , the piezoelectric device became 1 of Embodiment 7 is configured in the same manner as in Embodiment 1. The piezoelectric constant was calculated in the same manner as in Embodiment 1. Ec-, Ec +, γ and EuI of the piezo layer 82 (BNT) were 0.25 kV / mm, 0.53 kV / mm, 0.081 and 60 kV / mm, respectively.

(Embodiment 8)

Using the same piezoelectric element 80 as in Embodiment 7, the piezoelectric device was constructed 1 of the embodiment 8 configured. The current monitoring circuit 30 in the piezoelectric device 1 was set in the same manner as in Embodiment 2 in this case. The piezoelectric constant was determined in the same manner as in the embodiment 1 calculated.

(Embodiment 9)

Using the same piezoelectric element 80 as in Embodiment 7, the piezoelectric device was constructed 1 of the embodiment 9 configured. The driving circuit 20 in the piezoelectric device 1 was set in the same manner as in Embodiment 3 in this case. The piezoelectric constant was calculated in the same manner as in Embodiment 1.

(Comparative example 3)

Using the same piezoelectric element 80 as in Embodiment 7, the piezoelectric device was constructed 1 of Comparative Example 3 configured. The driving circuit 20 in the piezoelectric device 1 in this case was set in the same manner as in Comparative Example 1-3. The piezoelectric constant was calculated in the same manner as in Embodiment 1.

(Examples 10 to 17)

The material (K _{0, 5} Na _{0. 5)} NbO ₃ for the piezoelectric layer 82 was deposited under a temperature 700 ° C, in order to change the film thickness. The film thickness of the piezo layer 82 (KNN3) was 1.0 µm, 1.4 µm, 1.6 µm, 2.1 µm, 2.5 µm, 2.9 µm, 3.1 µm and 3.5 µm, respectively . The elements other than the piezo layer 82 configured the piezoelectric device 1 of Embodiments 10 to 17 as in Embodiment 3. The piezoelectric constant was calculated in the same manner as in Embodiment 1. Ec-, Ec +, y and EuI of the piezo layer 82 were approx. 0.8 kV / mm, 0.4 kV / mm, 0.088 and 100 kV / mm, respectively.

Table 1 shows the results of measurement of Pm ', Pr', (Pm'-Pr ') / 0.1, Ec-, Ec +, 5Ec + and 50Ec + of the piezo element used in Comparative Examples 1-1 to 1-3, 2 and 3 as well as in the exemplary embodiments 1 to 17, the film thickness t of the piezo layer, the EII and EuI obtained from the current monitoring circuit of the piezo element, the Emin and Emax obtained from the drive circuit, and the piezoelectric constant -d31.

The piezoelectric device 1 of Embodiments 1 to 17 in which the driving electric field was controlled to a predetermined value by the driving circuit 20 was given a higher piezoelectric constant than the piezoelectric device in Comparative Examples 1-1 to 1-3, 2 and 3 without this condition. This confirmed that the piezoelectric device 1 of the present invention is driven in the range in which the displacement with respect to the electric field can be achieved more efficiently.

The piezoelectric device 1 of embodiments 2, 3, 5, 6, 8, 9 to 17, which has a means that the positive electric field in the direction with a small absolute value of the electric coercive field and the negative electric field in the direction with a large absolute value of the electric Coercive field applied, obtained a higher piezoelectric constant than that of the piezoelectric device 1 of the exemplary embodiments 1 , 4 and 7. This confirmed that these piezoelectric devices are driven in the electric field area where the amount of displacement of the piezo element is larger because larger displacements are presumably due to the rotation of the electric dipole in the domain of the crystal particles can be obtained.

The piezoelectric devices 1 in Embodiments 3, 6, 9 to 17, which set the minimum value Emin of the driving electric field to more than five times Ec + and the maximum value Emax of the driving electric field less than fifty times Ec +, achieved an even higher piezoelectric constant. From this, it was confirmed that the piezoelectric devices are driven by the displacement due to the rotation of the electric dipole in the domain of the crystal particles in the area of the electric field where the amount of displacement of the piezo element is even larger.

In Embodiments 10 to 17, there was a tendency that the piezoelectric constant increases as the film thickness of the piezoelectric layer 82 increases from 1.0 µm and that the piezoelectric constant decreases from 2.5 µm. This is due to the fact that the increase in the film thickness of the piezo layer 82 promotes an improvement in the crystallinity and an increase in the piezoelectric constant, but the crystallinity of the first electrode layer 81 can no longer be adopted from around 2.5 μm, and then the crystals multiply with different orientations.

In addition, the sufficiently high piezoelectric constant can be realized with the piezoelectric device using a circuit that controls the driving electric field in an appropriate range.

The preferred embodiments according to the invention have been explained above. However, the present invention is not restricted to the above embodiments, but can be expanded within the scope of the inventive intention by various changes which of course also belong to the present invention.

For example, in the above embodiments, the current monitoring circuit 30 is provided in addition to the driver circuit 20. The current monitoring circuit 30 is not absolutely necessary, however. This is because the effect of the present invention can be obtained even in the configuration without the current monitoring circuit 30 if an appropriate range for the driving electric field of the piezoelectric element 80 can be confirmed by a probe measurement and so on. In that case, the switching means 40 is of course unnecessary.

Incidentally, in the above exemplary embodiments, the piezo element 80 was driven using the drive circuit 20 and the external power source 51. However, it is also possible to drive the piezo element 80 using a different power source of the piezoelectric device.

List of reference symbols

1

piezoelectric device

200

Head arrangement

300

Piezo actuator

700

Hard disk drive

800

Ink jet printer apparatus

Claims (7)

Piezoelectric device with a piezo element comprising a piezo layer and electrode layers, between which the piezo layer is arranged, and with a driver circuit that applies an electric driver field with alternating current via the electrode layers to the piezo layer, the polarizability γ of the piezo layer when an electric field is applied up to Saturation polarization is less than 1 × 10 ^-9 (C / (V · m), characterized in that the driver circuit has a means that sets the minimum value of the electrical drive field to be greater than the positive electrical coercive field of the piezo layer, and a means that sets the Maximum value of the electric driver field to less than (Pm '(maximum value of the polarization) - Pr' (quasi-residual polarization)) / (1 × 10 ^-9 ), the polarizability y = (Pm (saturation polarization) - Pr (residual polarization )) / Ed (maximum value of the applied electric field). Piezoelectric device according to Claim 1 , characterized in that the piezo layer on the positive and negative side of the electric field each comprises an electric coercive field, and that the driver circuit has a means that a positive electric field in the direction with a small absolute value of the electric coercive field and a negative electric field is applied in the direction with a large absolute value of the coercive electric field. Piezoelectric device according to Claim 1 , characterized in that the driver circuit has a means which sets the minimum value of the electrical driver field to more than five times the positive electrical coercive field of the piezo layer and the maximum value of the electrical driver field to less than fifty times the positive electrical coercive field of the piezo layer. Piezoelectric device according to Claim 1 , characterized in that the piezo layer of the piezo element consists of potassium sodium niobate. Piezo actuator using a piezoelectric device according to Claim 1 . Hard disk drive with a piezo actuator Claim 5 . Inkjet printer apparatus with a piezo actuator according to Claim 5 .

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